RF engineers attempt to design wireless networks so as to maximize the user experience while minimizing the cost to create that experience. Because of the natural usage patterns associated with devices that connect to these networks, the network devices are typically oversubscribed in an attempt to improve data throughput for the same relative cost. Oversubscribing refers to the situation where a network provider/ISP sells more collective bandwidth to customers than the network can technically provide based on the extremely low likelihood that all of the customers will be using all of their devices and all of their purchased bandwidth at the same time.
In order to measure the level of oversubscription in a network at a specific time and/or at a specific node of the network, a variable commonly referred to as a “oversubscription factor” (OSF) is typically used. This measure refers to the ratio of the allocated bandwidth per user to the guaranteed bandwidth promised to the user. The fact that the former value is a multiple of the latter value is a reflection of the reality that statistically few users will attempt to utilize their allocated bandwidth simultaneously.
ISPs and other network operators typically used a fixed OSF as a design factor associated with all or specific portions of the network. In typical deployments, the OSF value may range somewhere from 20 to 50. A busy network (i.e. one with significant loading and contention) would typically have a lower OSF such as 20, while a lightly loaded network (i.e. one with less loading and contention) might have a higher OSF in the range of 50 or so.
The OSF is used in network planning also to estimate the number of simultaneously active users on the network or at various nodes of the network. What is known as Average User Experience or Speed may be defined as the Total Capacity of the network or node divided by the number of simultaneous active users in the network or the applicable node. The number of simultaneous active devices can thus be calculated as follows:
      Simultaneous    ⁢                  ⁢    Active    ⁢                  ⁢    Devices    =            Total      ⁢                          ⁢      Devices        OSF  And the user experience can be calculated as:
      User    ⁢                  ⁢    Experience    =      Capacity          Simultaneous      ⁢                          ⁢      Active      ⁢                          ⁢      Devices      
For most network planning applications, a fixed OSF value has been generally acceptable. However, the use of a fixed OSF value does not take into account or address a varied device mix within a network such as in a wireless network. For example, a wireless network may be accessed a mix of large number of fixed modems, and a large number of smartphones. Fixed modems typically are used within the home as the primary source of the occupants' access to internet including many broadband based applications requiring the transfer of large amounts of data. On the other hand, smartphones are mobile devices that typical consume significantly lesser amounts of data. Hence, the OSF of a cell site wherein Fixed Modems dominate the device mix would be low, while the OSF of a cell site where Smartphones are more prevalent would be significantly higher. As a result, when a fixed OSF value is assumed, actual network behavior can and does deviate, sometimes drastically, from forecasted behavior.
In a modern wireless network with hundreds or thousands of cell sites and with a device mix consisting of a wide variety of devices each with different usage patterns and data demands, a fixed OSF calculation leaves much to be desired. For cell sites with less loading and contention, a fixed OSF may be too high for that particular node and therefore planning could be impacted both in terms of an over allocation of resources as well as a user experience which deviates from the expected experience. Alternatively, at cell sites where there is significantly more traffic (such as those with a fixed modem heavy usage pattern), the selected fixed OSF may be too low to be effective for the specific device mix and the user experience may be significantly degraded from expectations.